"It's like a keyword search," said Carla Brodley, co-developer of the program and an associate professor of computer engineering at Purdue. "You pose a query and it searches a database. We're doing the same thing with images."

Here's how it works: A physician uses a mouse to identify up to five diseased regions on a patient's image, then submits the picture in the form of a database query.

The software applies a series of image-processing algorithms to characterize the region and compares it with other images in the database.

The physician receives four pictures from the database, which can be enlarged, isolated, enhanced, and cross-sectioned. Doctors would also have access to the treatment histories of the database cases to aid in making a diagnosis.

Currently, the database contains only scans of human lungs, but researchers hope to eventually include magnetic-resonance images (or MRIs), of the knee, liver, and brain.

The system is designed to help doctors who are unfamiliar with certain diseases make more informed diagnoses.

"There's a big difference in expertise between a lung specialist and a plain old radiologist," Brodley said. "We're trying to improve diagnosis."

Normally, radiologists must sift through large books of compiled CT scans in order to compare cases. But the new retrieval system allows computers to analyze images in ways that once required the seasoned eyes of skilled radiologists.

With the increase of new programs such as computer-assisted mammograms that help doctors in image interpretation, some radiologists fear that all this technology might one day edge them out of their own profession.

"Eventually you'd have lower-salaried individuals doing the work that a high-priced, highly trained radiologist could do," said Dr. Charles Anderson, an associate professor of radiology at University of California at San Francisco. "If a hospital director could get a nurse to do it, pay them half the amount, and get the same work out of it, I think that's where it's headed."

But other physicians said they see no threat.

"It's going to be an awfully long time before a machine can replace a pair of eyes in interpreting any kind of image," said Dr. E. Stephen Amis Jr., professor of radiology at the Albert Einstein College of Medicine. "What radiologists are trying to do is to improve the accuracy of their interpretations. Computers are going to help us."

Brodley said that the Purdue retrieval program was designed to complement, not compete with, doctors.

"We're not trying to do automated diagnosis at all," said Brodley. "We're just trying to provide a resource to find more information."

A paper on the program will be published in the July issue of the journal Computer Vision and Image Understanding.